The present invention refers to polymer foams, more particularly to low density aromatic polymer foams prepared using a mixture of halogen-free blowing agents and to a process for preparing same.
Styrene polymer foams are widely used in the fields of construction, civil engineering and thermal insulation. The styrene polymer foam suitable for such applications desirably has relatively small cells and dimensional stability. These foams are the so-called extruded foams. Extruded foams are also employed in the so-called decorative field wherein a foam plank may be cut into a decorative foam and be used as is or used as a base for further decorative material. Particularly desirable stable styrene polymer foam is obtained employing the method set forth in U.S. Pat. No. 3,960,792 to M. Nakamura.
Extruded foams and their manufacture are discussed in U.S. Pat. Nos. 2,409,910; 2,515,250; 2,669,751; 2,848,428; 2,928,130; 3,121,130; 3,121,911; 3,770,688; 3,815,674; 3,960,792; 3,966,381; 4,085,073; 4,146,563; 4,229,396; 4,312,910; 4,421,866; 4,438,224; 4,454,086 and 4,486,550. For a considerable period of time, styrene polymer foams have been extruded employing a variety of organic blowing agents, such as chlorofluorocarbons (CFC's), chlorofluorohydrocarbons HCFC's and other halogenated hydrocarbons as well as mixtures thereof. An alternative blowing agent system utilizing carbon dioxide and an alkane is set forth in U.S. Pat. Nos. 4,344,710 and 4,424,287; the teachings of which are incorporated herein by reference.
Due to increased environmental concerns about ozone depletion, green house effects and air quality in general, large efforts are being made to replace CFC's, HCFC's and other halogenated hydrocarbons currently used as blowing agents in the foam industry with environmentally more acceptable blowing agents.
It remains highly desirable to provide a process for preparing a low density aromatic polymer foam using a halogen-free blowing agent. Furthermore, it also would be highly desirable to provide a low density aromatic polymer foam prepared using a halogen-free blowing agent.